1. Field of the Invention
This invention relates to a continuous electroplating machine for plating the tabs or terminals along one edge of a rectangular plate such as a printed circuit board, as the boards are conveyed through the machine. This invention has an improved conveyor means and improved mechanical masking means.
2. Description of the Prior Art
It is known in the electroplating art to cover portions of a printed circuit board which should not be plated with a thin synthetic resin film and the peripheral portions are masked with adhesive tapes, and the board is dipped in a level controlled electroplating solution and charged with electricity for plating.
The printed circuit board terminals are copper plated and they need to be furnished with a hard wear resistant surface having good electrical conductive properties by first applying a nickel plating and then a gold plating to the terminals.
This dipping method is slow and it requires preliminary preparations prior to the plating operation which adds to the cost of labor and materials. Plating at a high current density is impossible for the dipping method so that it takes a long period of time to obtain the required thickness of the plated deposit. This dipping method is further defective in that the thickness of the plating deposit is often uneven depending upon the location of the object to be plated, the distance between the anodes and cathodes, the condition of the electrolyte agitation and because all of these conditions are very hard to control.
The recent Higuchi et al U.S. Pat. No. 4,029,564 describes a batch feed, electroplating machine for gold plating the terminals of printed circuit boards, one board at a time. This prior art plating machine uses a mechanical masking means to protect the portions of the PC board not requiring plating. This masking means comprises a pair of opposed plates having masking sheets on the facing sides thereof, and pressure cylinder means coacting with the plates for clamping the PC board therebetween. This patent also has replaced the old dipping method of plating the terminals by jetting the plating solution onto the board terminals. This Higuchi et al machine is a one step process machine and it fails to provide a continuous movement of boards through the machine for complete processing; including stripping, cleaning, activation, plating and rinse cycles. Also the Higuchi et al machine fails to provide quick equipment interchangeability to handle the processing of boards of various thicknesses and sizes. Moreover, this prior art design does not provide absolute shielding or masking of board side edges from plating solutions. These exposed edges allow tin-lead contamination to enter the solution which eventually leads to serious damage to the plating baths. Likewise the method of solution movement in the Higuchi et al. machine lends itself to localized "richness" in comparison to the method of the present invention which encourages uniform metal content distribution over the full length of the manifold.
In the Johnson et al U.S. Pat. No. 3,723,283 there is a plating system for a continuous strip or web of work material rather than individual sheetlike workpieces as are accomodated by the plating machine of the present invention. In FIGS. 11 and 12 of this Johnson et al. patent the continuously moving web passes between two flexible belt-like gaskets which are not motor-driven, but merely free wheeling so as to be trackable over the surfaces of the web. The gaskets have apertures, and there is an electrolyte entrance header within one gasket and an electrolyte exit header within the other gasket to the electrolyte passes through one gasket, through the web and out through the other gasket whereby the gaskets shield or mask the web in areas that are not to be plated.
The Holte U.S. Pat. No. 3,966,581 shows apparatus for the continuous electroplating of selected portions of discrete electronic components. The components are carried by a conveyor belt which is electrically conductive and has spaced openings for receiving the component bodies in nesting relationship. An insulating belt sandwiches and thereby retains the components in their nested positions to maintain the achieved electrical continuity.